Air turbine starter with unitary inlet and stator

ABSTRACT

An air turbine starter for use in aircraft or other gas turbine engine applications. In a particular embodiment, the air turbine starter has a titanium unitary inlet structure. The unitary inlet structure has a housing having a longitudinal centerline. The housing defines an air inlet, a mounting surface, and a flow path therebetween. Integrally formed inside the housing and transverse to the longitudinal centerline is a stator for directing the flow of air in to the turbine blades of the turbine starter. The stator has a central circular body with a plurality of angularly spaced circumferentially mounted stator fins. An improved unitary inlet structure and method for making such a unitary inlet and stator are also provided.

FIELD OF THE INVENTION

This invention relates generally to air turbine starters for gas turbineengines, and, in particular, to the air turbine stator inlet assemblyused in such starters.

BACKGROUND OF THE INVENTION

An air turbine starter is a device used to start a turbine engine, suchas a gas turbine jet engine commonly found on aircraft. The air turbinestarter is connected to the jet engine and is used to start the jetengine in generally the same way as a starter for an automobile is usedto start the automobile's engine. The developer of the presentinventions, Honeywell International, Inc., has for years successfullydesigned, developed, manufactured and repaired air turbine starters.

FIG. 1 shows a partial cut-away diagram of a conventional air turbinestarter 100, which includes an air inlet assembly 103 that is joined toa main housing 105. Maintained within the main housing 100 are airwaysand other components such as a turbine assembly 107, an air outlet 109,and a gearbox 111 which is coupled to an output shaft (not shown). Theturbine assembly 107 has a turbine wheel 113 with circumferentiallymounted blades 115, a rotatable drive shaft 117 and a gear 119. The airinlet assembly 103 is made up of two primary components, a stator 121and an outer shell 123. In many instances the stator 121 and outer shell123 provide mating threads 125. In some cases a locking pin 127 mayadditionally be used to assist in keeping the stator 121 and outer shell123 together. Additional turbine starter features are disclosed inHoneywell's U.S. Pat. No. 6,318,958 (Giesler et al.) and U.S. Pat. No.4,914,906 (Burch) which are incorporated by reference herein.

In order to start a jet engine the air turbine starter 100 is firstactivated. Generally speaking, such activation is accomplished byconnecting an air pressure duct to an air inlet 129 provided by thestator 121 portion of the inlet assembly 103. Compressed air is directedby contoured passage 131 through stator fins 133, across the turbineblades 115 and is vented from air outlets 109. In operation, the energyof the moving air is converted by the blades 115 into rotary motion,causing the turbine assembly 107 to rotate.

Generally, the turbine starter 100 is joined to the jet turbine enginesuch that it travels with the jet. As a result, the weight of theturbine starter 100 is generally a calculated component of the overallweight of the aircraft and as such, reduces the total amount of cargoweight that the jet may transport. In the commercial aircraft industry,each additional pound of weight may cost the aircraft manufacturer afinancial penalty. Likewise each additional savings of a pound may becredited to the manufacturer as a financial savings.

As noted above, the inlet assembly 103 is comprised of two components,namely the stator 121 and outer shell 123. The function of the statorfins 133 is to direct the supplied compressed air across the turbineblades. The narrowing passageways between the stator fins 133 act asnozzles to increase the velocity of the air as it strikes the rotatingturbine blades 115. Given the velocity and pressure of the compressedair, it is generally desirable to align the direction of the air flow tothe turbine blades 115 so as to reduce stress and wear upon the turbineassembly. The outer shell 123 generally aligns the stator fins 133 tothe turbine blades 115 and provides the outer portion of the contouredpassage 135 leading to the air outlets 109.

The manufacture of the air inlet assembly 103 is typically an involvedtooling process given the nature of the air inlet 129, the contouredpassage 131, and configuration of the stator fins 133. As the namesuggests, the stator 121 and the stator fins 133 do not rotate.Typically the outer shell 123 may be fabricated as a single piece from atitanium alloy, desired for it's strength and relative light weight aswell as other characteristics.

Manufacture of the stator 121 as a single item from a titanium alloy hasheretofore not been achievable. The contours, airfoil shapes and limitedspaces have frustrated attempts to produce simply the stator 121, letalone the outer shell 123 and stator 121 as a single contiguous item. Asa result, the stator 121 is generally manufactured from a heavier, buteasier to tool alloy such as an inconel alloy. Several machining stepsmay be needed to join the stator 121 to the outer shell 123, each steppotentially resulting in additional training, equipment, cost, and time,as well as potentially different geographic locations of each step offabrication—a factor adding yet further cost for time and shipping. Inaddition, the outer shell 123 may be flared out or fabricated withadditional sidewall thickness in the area accommodating the matingthreads 121. As such, the inlet assembly 103 weight as thickened may begreater than what could be achieved with a unitary inlet assembly.Further, as the outer shell 123 and stator 121 are fabricated fromdifferent metal alloys, the different relative hardness and thermalexpansion and contraction properties may frustrate the threaded unionand accelerate wear between the components.

Wear of the stator fins 133 and turbine blades 115 is understood to be anatural result of starter operation. In certain instances, internalvibration and or dynamic responses of the turbine blades may result infracturing of the turbine blades 115, also known as mouse bites. Theoccurrence of occasional mouse bites to the turbine blades 115 maydecrease operational performance, cause internal damage, and/oraccelerate the need for maintenance. The common practice of setting thejoined stator 121 and outer shell 123 with a locking pin 127 has beenfound to occasionally fail. Operational vibration of the aircraft,thermal expansion and contraction, and or perhaps even installationerror may introduce the end 137 of the locking pin 127 into thecontoured passage 131, an event that may or may not affect theperformance of the starter. Should the locking pin 127 come loose duringoperation and entirely enter the passage 131, passage of the pin 127through the stator fins 133 and or the turbine blades 115 may causesignificant damage to these components and affect the overall functionand performance of the turbine starter and may necessitate a moreextensive rebuild of the turbine starter 100.

However, it should be appreciated that despite the drawback of mousebites and the potential failure of the locking pin 127, air turbinestarters are generally operationally safe and reliable. Inspections ofthe air inlet 129 and stator 121 are generally part of the routinemaintenance schedules set for the turbine starter 100.

Hence, there is a need in for an improved air turbine starter having aninlet and stator with improved characteristics to overcome one or moreof the drawbacks identified above. The present invention satisfies oneor more of these needs.

SUMMARY OF THE INVENTION

The invention provides an air turbine starter with an improved unitaryinlet structure for gas turbine applications, and an associated improvedunitary inlet structure.

In particular, and by way of example only, one embodiment of the presentinvention provides an air turbine starter having a main housing, aturbine assembly partially disposed within the main housing and aunitary inlet structure. The turbine assembly includes a turbine wheelhaving a plurality of circumferentially mounted blades. The unitaryinlet structure is coupled to the main housing and substantiallyencloses at least a portion of the turbine wheel. The unitary inletstructure is characterized by a housing section having at least aninlet, an inner surface, and a mounting surface. A stator section isdisposed at least partially within the housing section and has an outersurface. At least a portion of the housing section inner surface and atleast a portion of the stator section outer surface form a flow paththat fluidly couples the housing section air inlet to the turbineblades.

Moreover, according to an embodiment thereof, the invention provides anair turbine starter unitary inlet structure. The unitary inlet structureis characterized by an annular housing having a longitudinal centerline.The housing defines an air inlet, an inner surface and a mountingsurface. An annular air director is provided integrally formed as partof the annular housing, the annular air director disposed at leastpartially within the annular housing and having an outer surface. Atleast a portion of the annular housing inner surface and the airdirector outer surface form a flow path that extends substantiallyparallel to the longitudinal centerline.

In yet another embodiment, the invention may provide a titanium airturbine starter unitary inlet structure. The titanium unitary inletstructure is characterized by a housing having a longitudinalcenterline, an air inlet, an inner surface, a mounting surface, theannular housing defining a flow path between the air inlet and themounting surface. A stator is integrally formed as part of the housing.The stator is disposed at least partially within the housing between theinlet and mounting surface and substantially transverse to thelongitudinal centerline.

In optional details, the stator may be further characterized by acentral circular body with a plurality of angularly spacedcircumferentially mounted stator fins. The stator fins may be also beasymmetrically spaced.

In still another embodiment, the invention provides a method ofmanufacturing a titanium air turbine starter unitary inlet structure.The method includes casting a unitary inlet structure from an alloy. Thecast unitary inlet structure is initially characterized by an oversizedannular housing having a longitudinal centerline, at least an air inletand a mounting surface. An oversized stator integrally formed as part ofthe oversized annular housing. The oversized stator is disposed at leastpartially within the housing and has a plurality of angularly spaced,circumferentially mounted oversized stator fins connecting the stator tothe annular housing. The oversized housing and stator are chemicallymilled to remove alloy from the oversized surfaces. The clearancebetween the chemically milled stator fins is measures and compared toone or more predetermined values. The chemical milling and measuringsteps are repeated until at least the measured clearance between thechemically milled stator fins is substantially equal to one or morepredetermined values.

These and other features and advantages of the preferred apparatus andmethod will become apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings which illustrate, byway of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial cross-sectional view of a prior art turbine starterwith a two-piece stator inlet assembly;

FIG. 1B is an enlarged cross-sectional view of the threaded attachmentof the prior art assembly shown in FIG. 1A;

FIG. 2 is a partial cross-sectional view of a an air turbine starterwith a the unitary inlet structure according to an embodiment of thepresent invention;

FIG. 3A is a half cutaway of the unitary inlet structure shown in FIG.2;

FIG. 3B is a partial cutaway of the unitary inlet structure shown inFIG. 2;

FIG. 4 is a perspective view of the unitary inlet structure shown inFIGS. 3A and 3B;

FIG. 5 is an exterior view of the unitary inlet structure shown in FIG.4;

FIG. 6 is an interior view of the unitary inlet structure shown in FIG.5;

FIGS. 7A through 7C illustrate the steps of making the unitary inletstructure as shown in FIGS. 3A and 3B.

DETAILED DESCRIPTION

Before proceeding with the detailed description, it is to be appreciatedthat the present invention is not limited to use or application with aspecific type of air turbine starter. Thus, although the presentinvention is, for the convenience of explanation, depicted and describedwith respect to one type of unitary air turbine stator inlet as may beused in connection with a gas turbine engine, this invention may beapplied to other types and styles of air turbine starters used in otherturbine engine applications.

A partial cut-away view of an exemplary air turbine starter 100employing an embodiment of the present invention is shown in FIG. 2. Asshown herein, air turbine starter 100 includes a main housing 105, agearbox 111 a turbine assembly 107, a unitary inlet structure 200, andat least one air outlet vent 202. The gearbox 111 is coupled to anoutput shaft (not shown), which is in turn coupled to, for example, aturbofan jet engine. The turbine assembly 107 includes a turbine wheel113 with circumferentially mounted blades 115 and a rotatable driveshaft 117 that extends into the main housing 105 and is joined to gear119 and gearbox 111.

The unitary inlet and stator, more simply identified as the unitaryinlet structure 200 includes a housing section 204 with an interiorsurface 228 defining an air inlet 206, a mounting surface 208, and aflow path (represented by arrows 210) for conveying a flow of airtherebetween. In at least one embodiment the housing 204 is an annularhousing about a longitudinal centerline 212. The longitudinal centerline212 may substantially match to the longitudinal centerline of the driveshaft 117. An annular air director 214, such as a stator 216 isintegrally formed as part of housing 204 proximate to the inlet 206.More specifically the air director 214 is disposed at least partiallywithin the housing 204, substantially transverse to the flow path 210and concentric to the longitudinal centerline 212. The stator 216 has anouter surface 230 that, along with the inner surface 228 of the housing204, further forms and defines flow path 210. More specifically, atleast a portion of the inner surface 288 of the housing 204 and aportion of the outer surface 230 of the stator 216 fluidly couple theair inlet 206 to the turbine blades 115.

The mounting surface 208 is shaped and sized to join the unitary inletstructure 200 to the main housing 105, such that the stator 216 ispositioned proximate to the upstream side 218 of turbine wheel 113 Inaddition, the turbine wheel 113 is substantially enclosed by the unitaryinlet structure 200. The outlets 202 are located proximate to thedownstream side 220 of the turbine wheel. Under appropriatecircumstances, outlets 202 may be provided as part of the unitary inletstructure 200 housing 204 rather than the main housing 150 of thestarter 100. As conceptually illustrated, the unitary inlet structure200 and main housing 105 define a flow path through passage 222.Compressed air entering the inlet 206 is channeled by passage 222through the stator 216, through the blades 115 of the turbine wheel 113,and to the outlet 202.

The joining of the unitary inlet structure 200 to the main housing 105may be accomplished by the any one of numerous forms of attachers suchas, for example a threaded screw sockets 300 (see FIG. 3), set toreceive bolts 224 extending from the main housing 105. Under appropriatecircumstances, other suitable alternative joining methods may beemployed. Generally, attaching bolts 224 and outlet vents 202 alternatein their placement about the exterior of the main housing 105. Underappropriate circumstances a bolt 224 may pass through a portion of theoutlet 202, or the outlet 202 may provide access to the attaching bolt224.

The advantages of the unitary inlet structure 200 may be furtherappreciated with respect to the views provided in FIGS. 3 through 6. Theperspective view of FIG. 4, along with the exterior view of FIG. 5 andinterior view of FIG. 6 are provided to complement FIGS. 3A and 3B. Asindicated in the cutaway depictions of FIGS. 3A and 3B, the housing 204and stator 216 are advantageously formed as a unified whole. There areno threads, welds or other forms of attachment joining separately formedcomponents as in the prior art. Indeed, the term “unitary” as usedherein with respect to the unitary inlet structure 200 is understood andappreciated to define the structure as an undivided whole, and not oneassembled from a collection of separately manufactured parts. As isdescribed in greater detail below, the unitary inlet structure 200 ispreferably manufactured from a titanium alloy.

In at least one embodiment, the stator 216 is characterized by a centralcircular body 302 with a plurality of angularly spaced circumferentiallymounted blades, commonly referred to as stator fins 304, stator bladesor stator veins. As shown, the stator fins 304 may exist at about themidpoint between the air inlet 206 and the mounting surface 208. In atleast one embodiment the stator fins 304 are substantially identical.

The central body 302 may be described as somewhat parabolic in shapesuch that the center-point 306 is extended towards the air inlet 206.More specifically, the central body 302 serves to assist in defining theflow path 210, directing the supplied compressed air into the statorfins 304. As shown in FIG. 3A, as the surface of the central body 302expands from the center-point 306 to the stator fins 304, the definedpassage 308 (the first part of flow path 202 shown in FIG. 2) narrows.This narrowing of the passage 308 serves to further compress andincrease the air velocity as it is directed into the stator fins 304.

To assist and insure proper flow of the directed air through the turbineblades 115, the stator 216 may additionally include an outer ring 310.When the unitary inlet structure 200 is mounted to the main housing 105,the outer ring 310 may encompass at least a portion of the distal edges226 the turbine blades 115 (see FIG. 2). Improper placement of thestator 216 relative to the turbine blades 115 may result ininappropriate air flow between the stator and the turbine andcorrespondingly lower the turbine starter 100 performance.

As the prior art assembly requires the stator 121 and outer shell 123 tobe joined, such as by mated threading 125, substantially exact placementof the stator 121 relative to the turbine blades 115 may not beconsistently achieved. Tooling issues in the threading process mayresult in the stator 121 being either too close or too removed from theturbine blades 115. An advantageous result of the unitary constructionherein disclosed, is the substantially exact and consistent placement ofthe stator 216 relative to the turbine blades 115 when the unitary inletstructure 200 is attached to the main housing 105.

To further enhance the velocity of the air as it drives through theturbine blades 115, the stator fins 304 may have a cross-sectional shapeof an air-foil 320 (see FIG. 3B). In general, the leading edge 322 ofeach stator fin exists in a common plain 326 transverse to thelongitudinal centerline 212. In a similar fashion, the trailing edge 324of each stator fin exists in a common plain parallel to the plaindefined by the plurality of leading edges 322.

During operation of the air turbine starter, compressed air is suppliedto the air inlet 206, generally with the use of a flexible hose. Toassist with the attachment of a hose, the unitary inlet structure 200may include a flanged skirt 312 or other suitable structure to which asupply hose may readily be attached. The non-moving, rigidly mountedstator fins 304 serve in part to shelter the turbine assembly 107 fromthe direct brunt of the potentially non-uniform thrust force provided bythe compressed air as it exits the supply hose and enters the air inlet206. The compressed air is directed by the passage 308 to arrive at thestator fins 304 with an alignment of flow that is substantially parallelto the longitudinal centerline 212. Relative to this flow of oncomingair, the stator fins 304 are oriented with an angle of attack touniformly align the flow of air for delivery into the turbine blades115. It is understood and appreciated that an angle of attack of an,such as one of the turbine blades 115, is the angle at which therelative wind meets the airfoil. In at least one embodiment, the angleof attack is about 36.738 degrees. Further, in at least one embodimentthe angular spacing of the stator fins 304 may be symmetric.

As noted above, prior art turbine starters have been found to experienceoccasional mouse bites to the turbine blades 115. According to at leastone embodiment of the present invention, the harmonics created by theair passing from the stator 216 through the turbine blades 115 whichcreate the environment for mouse bites to occur may be substantiallyprevented. Specifically, according to at least one embodiment of thepresent invention, the angular spacing of the stator fins 304 isasymmetric. The asymmetric spacing of the stator fins 304 inducesdifferent portions of the stator 216 to deliver air to the turbineblades 115 slightly differently. As an engineer might generalize to alayperson, the turbine wheel is fooled during it's rotations—at onemoment in the revolution the blades 115 receive air from a stator 216appearing to have one number of stator fins 304, and at the next momentappearing to have a different number of stator fins 340. Suchdifferences in air delivery are sufficient to disrupt and/or otherwiseprevent the formation of potentially harmful harmonic frequencies in theturbine blades 115.

The asymmetric angular spacing of the stator fins 304 may be more fullyappreciated with reference to FIG. 6. The stator fins 304 may besubdivided into at least three groups. The first group 600 of statorfins 304 may be characterized by substantially equal angular spacing 602for about the total number of overall stator fins plus at least one, thespaced arrangement forming a first arc 604 having a first end 606 and asecond end 608.

The second group 610 of stator fins 304 may be characterize bysubstantially equal angular spacing 612 for about the total number ofoverall stator fins minus at least one, the spaced arrangement forming asecond arc 614 having a first end 616 and a second end 618. A transitiongroup 620 characterized by an even number of stator fins 304substantially equal in angular spacing 622 for about the total number ofstator fins 304. The transition group 620 serves to transition thespacing from the first group 600 to the second group 610, and from thesecond group 610 back to the first group 600. More specifically, in atleast one embodiment one half of the transition group 620, for examplestator fin 624, is placed between the second end 608 of the first arc604 and the first end 616 of the second arc 614. In similar fashion, thesecond half of the transition group 620, for example stator fin 626, isplaced between the second end 618 of the second arc 614 and the firstend 606 of the first arc 604. This arrangement of the first group 600,second group 610 and transition group 620 substantially forms a circle.

As shown, in at least one embodiment the stator 216 comprises 29 statorfins 304. In addition, in at least one embodiment the number of statorfins 304 in each of the above described groups may be as follows; thefirst group 600 consisting of 14; the second group consisting of 13; andthe transition group consisting of 2. The angular spacing 602 of thefins of the first group 600 (stator fins 304 1 through 14) is about12.0000 degrees. The angular spacing 612 of the fins of the second group608 (stator fins 304 16 through 28) is about 12.8571 degrees. Theangular spacing 622 of the transition group 622 (stator fins 304 15 and29) is about 12.4286 degrees.

As used herein, the term angular spacing is to be understood andappreciated to imply angular increments about the circumference of acircle. For example, placing 12 points at the angular spacing of 30degrees along the circumference of a circle will provide the hour marksas are commonly seen on traditional non-digital clocks. Moreover, asmeasured from a consistent point, one stator fin to the next (leadingedge 322, trailing edge 324 or other reference point), if stator fin A′is to be angularly spaced 12.0000 degrees from stator fin A, the leadingedge 322 of stator fin A′ will be 12.0000 degrees from the leading edge322 of stator fin A.

In addition to the precise placement of the stator 216 relative to theturbine blades 115 as discussed above, the unitary inlet structure 200provides numerous additional benefits. Manufacturing costs and time maybe reduced by eliminating the additional tooling required to thread thestator and housing components so that they may be joined. In addition,the use of a locking pin or other setting device that may inadvertentlycome loose and cause internal damage to the air turbine starter 100 iseliminated. Further, inventory, tracking, and purchase order issues aresimplified as a natural result from the reduction in component pieces.

The preferred embodiments of the unitary inlet structure 200 arepreferably achieved with a titanium unitary inlet structure 200. Morespecifically, fabrication of the unitary inlet structure 200 may byachieved with the use of a titanium alloy, such as a general purposetitanium alloy as is traditionally used in the aircraft industry forparts requiring a good strength-to-weight ratio and corrosionresistance.

In at least one embodiment, the titanium alloy commonly known andidentified as Ti6Al4V may be used. The unitary inlet structure 200 asfabricated from the titanium alloy may be significantly lighter thanprior art stator and inlet assemblies wherein the housing is fabricatedin titanium alloy, but the stator is fabricated from a heavier alloysuch as a common inconel alloy. In at least one embodiment the unitaryinlet structure 200 may be about 0.5 pounds lighter than conventionalprior art inlet and stator assemblies, an achievement that may translateto a savings of about $500 per takeoff to the aircraft operator.

Having described the individual components of the unitary inletstructure 200, a preferred method of fabricating a titanium unitaryinlet structure 200 will now be described as is illustrated in FIG. 7.It will be appreciated that the described method need not be performedin the order in which it is herein described, but that this descriptionis merely exemplary of one preferred method of fabricating a titaniumunitary inlet structure 200 in accordance with the present invention.

In at least one embodiment, fabrication involving casting may be used.With the use of casting there is no requirement that the stator 216, andmore specifically the stator fins 304 be separately manufactured,arranged and joined by an appropriate process. Casting advantageouslypermits the outer housing 204 and internal stator 216 to be formed ofsubstantially the same alloy and at substantially the same time.

As noted above, prior attempts to achieve a titanium unitary inletstructure 200 have been unsuccessful. To surmount this obstacle, in atleast one embodiment an oversized annular housing 704 having alongitudinal centerline 712 is cast. The oversized housing defines anair inlet 706, a mounting surface 708 and a flow path therebetween.Inside the housing 704 is integrally cast an oversized stator betweenthe air inlet 706 and mounting surface 708, substantially transverse toand concentric with the longitudinal centerline 712.

The internal cast stator is further characterized by a central circularbody with a plurality of angularly spaced circumferentially mountedoversized stator fins 752 connecting the stator to the housing 704. Inat least one embodiment the titanium alloy used in the casting iscommonly known and identified as Ti6Al4V. In at least one embodiment theangular spacing of the stator fins may be symmetrical. In at least onealternative embodiment the angular spacing of the stator fins may beasymmetrical, as described above.

It is understood and appreciated that as used herein, the term oversizedrefers to casting the unitary inlet structure 750 with excessthicknesses relative to the design specifications. It is to be furtherunderstood and appreciated that substantially all of the components areuniformly oversized. For example, if the cast stator fins 752 areoversized by about 2 millimeters in thickness, then so too is the casthousing 704 oversized by about 2 millimeters in thickness. As shown inFIG. 7A the clearance 754 between the freshly cast stator fins 752 maybe small, and below design specifications.

To remove the additional alloy from the oversized surfaces, the castoversized unitary inlet structure 750 are placed in a chemical bath 756.More specifically the oversized unitary inlet structure 750 may besuspended in a milling tank 758 containing an appropriate chemicalmilling solution 760 for the titanium alloy used in the casting. Underappropriate circumstances it may be desired to pre-clean the oversizedunitary inlet structure 750 to remove foreign materials such as oil,etc. Generally speaking, agitation of the milling solution 760 may occurduring the chemical milling process to improve exposure of the surfacesto the milling solution 760 as well as to maintain a balancedconcentration of the milling solution 760 throughout the tank 758.

The duration of the chemical milling process may be determined bycalculating the rate of alloy removal for the chemical milling agentemployed. Due to the precise clearance between the stator fins set forthin the design specifications, it may be desirable to calculate a firstduration sufficient to remove substantially about 50 to 90 percent ofthe oversizing alloy. Upon removal from the chemical bath 756, thetechnician may measure the clearance 762 between the chemically milledstator fins 764 of the chemically milled unitary inlet structure 766 andcompare the measured clearances to the design specifications providingone or more predetermined values.

From the measured clearance, the rate of removal may be recalculated andused to determine the duration for a repeat of the chemical millingprocess, if necessary, sufficient to provide clearance between thestator fins within design specifications. In at least one embodiment,the process of chemical milling may be repeated three times, the firstremoving substantially about 50% of the oversizing alloy, the secondremoving about 90% of the remaining oversizing alloy, and the thirdremoving substantially all of the remaining oversizing alloy to provideclearance 764 within design specifications. Moreover, the stator finsare chemically milled until at least the measured clearance between thechemically milled stator fins is substantially equal to one or more ofthe predetermined values set forth in the design specifications.

It is understood and appreciated that the components of the chemicallymilled unitary inlet structure 766 are substantially identical to theabove identified and discussed components of the unitary inlet structure200. Under appropriate circumstances, additional tooling may beperformed upon chemically milled unitary inlet structure 766, such as tofurther define the flanged skirt 312 and/or threaded sockets 300.

Chemical milling of the cast titanium unitary inlet structure permitsthe fabrication technician to achieve the required airfoil contours ofthe stator fins without requiring separate manufacture and installation.Reducing manufacturing time and costs, such single piece casting alsoaids in producing substantially identical titanium components resultingin more consistent and predictable turbine starter 100 performance.Maintenance upon the titanium unitary inlet structure is alsosubstantially reduced as it is generally not possible for the componentsto separate. Reductions in manufacturing costs may also permit a damagedstator and inlet to simply be recycled rather than re-manufactured.

While the invention has been described with reference to the preferredembodiment, it will be understood by those skilled in the art thatvarious alterations, changes and improvements may be made andequivalents may be substituted for the elements thereof and stepsthereof without departing from the scope of the present invention. Inaddition, many modifications may be made to adapt to a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Such alterations, changes,modifications, and improvements, though not expressly described above,are nevertheless intended and implied to be within the scope and spiritof the invention. Therefore, it is intended that the invention not belimited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An air turbine starter comprising: a main housing; a turbine assemblypartially disposed within the main housing, the turbine assemblyincluding a turbine wheel having a plurality of blades circumferentiallymounted thereon; and a unitary inlet structure coupled to the mainhousing and substantially enclosing at least a portion of the turbinewheel, the unitary inlet structure including: a housing section havingat least an inlet, an inner surface, and a mounting surface, themounting surface coupled to the main housing; and a stator sectionintegrally formed as part of the housing section, the stator sectiondisposed at least partially within the housing section and having anouter surface, wherein at least a portion of the housing section innersurface and at least a portion of the stator section outer surface forma flow path that fluidly couples the housing section air inlet to theturbine blades.
 2. The air turbine starter of claim 1, wherein theunitary inlet structure is manufactured from a Titanium alloy.
 3. Theair turbine starter of claim 1, wherein the unitary inlet structurecoupled to the main housing defines a flow path from the air inlet,through the stator, through the blades of the turbine wheel, and to theoutlet vent.
 4. The air turbine starter of claim 1, wherein the statoris characterized by a central circular body with a plurality ofangularly spaced circumferentially mounted stator fins.
 5. The airturbine starter of claim 4, wherein each stator fin presents an angle ofattack of about 36.738 degrees.
 6. The air turbine starter of claim 4,wherein the angular spacing of the stator fins is symmetrical.
 7. Theair turbine starter of claim 1, wherein the stator is characterized by acentral circular body with a plurality of asymmetrically angularlyspaced circumferentially mounted stator fins.
 8. The air turbine starterof claim 7, wherein the stator fins are subdivided into at least threegroups; a first group substantially equally angularly spaced for aboutthe total number of stator fins plus at least one, the spacedarrangement forming a first arc having a first and second end; a secondgroup substantially equally angularly spaced for about the total numberof stator fins minus at least one, the spaced arrangement forming asecond arc having a first and second end; and a transition groupcharacterized by an even number of stator fins substantially equallyangularly spaced for about the total number of stator fins; wherein onehalf of the transition group is placed between the second end of thefirst arc and the first end of the second arc, and the second half ofthe transition group is placed between the second end of the second arcand the first end of the first arc, thereby joining the first and secondarcs to substantially form a circle.
 9. The air turbine starter of claim7, wherein the stator is comprised of 29 stator fins.
 10. The airturbine starter of claim 9, wherein the angular spacing of stator fins 1through 14 is based on substantially equivalent spacing for about 30stator fins, the angular spacing of fin 15 is based on spacing for about29 fins, the angular spacing of stator fins 16 through 28 is based onsubstantially equivalent spacing for about 28 stator fins, and theangular spacing of fin 29 is based on spacing for about 29 fins.
 11. Anair turbine starter unitary inlet structure comprising: an annularhousing having a longitudinal centerline, an air inlet, an innersurface, and a mounting surface; and an annular air director integrallyformed as part of the annular housing, the air director disposed atleast partially within the annular housing and having an outer surface,wherein at least a portion of the annular housing inner surface and theair director outer surface form a flow path that extends substantiallyparallel to the longitudinal centerline.
 12. The unitary inlet structureof claim 11, wherein the annular air director is substantiallyconcentric to the longitudinal centerline.
 13. The unitary inletstructure of claim 11, wherein the annular air director is a statorcharacterized by a central circular body with a plurality of angularlyspaced circumferentially mounted stator fins.
 14. The unitary inletstructure of claim 13, wherein the spacing of the stator fins issymmetric.
 15. The unitary inlet structure of claim 13, wherein thespacing of the stator fins is asymmetric.
 16. The unitary inletstructure of claim 11, manufactured from a Titanium alloy.
 17. ATitanium air turbine starter unitary inlet structure comprising: ahousing having a longitudinal centerline, an air inlet, an innersurface, a mounting surface, the annular housing defining a flow pathbetween the air inlet and the mounting surface; and a stator integrallyformed as part of the housing, the stator disposed at least partiallywithin the housing between the inlet and mounting surface andsubstantially transverse to the longitudinal centerline.
 18. The unitaryinlet structure of claim 17, wherein the stator is characterized by acentral circular body with a plurality of angularly spacedcircumferentially mounted stator fins.
 19. The unitary inlet structureof claim 18, wherein each stator fin presents an angle of attack ofabout 36.738 degrees.
 20. The unitary inlet structure of claim 18,wherein the angular spacing of the stator fins is symmetrical.
 21. Theunitary inlet structure of claim 17, wherein the mounting surfacefurther comprises at least one attacher.
 22. The unitary inlet structureof claim 21, wherein the at least one attacher is a threaded screwsocket.
 23. The unitary inlet structure of claim 17, wherein the statoris characterized by a central circular body with a plurality ofasymmetrically angularly spaced circumferentially mounted stator fins.24. The unitary inlet structure of claim 23, wherein the stator fins aresubdivided into at least three groups; a first group substantiallyequally angularly spaced for about the total number of stator fins plusat least one, the spaced arrangement forming a first arc having a firstand second end; a second group substantially equally angularly spacedfor about the total number of stator fins minus at least one, the spacedarrangement forming a second arc having a first and second end; and atransition group characterized by an even number of stator finssubstantially equally angularly spaced for about the total number ofstator fins; wherein one half of the transition group is placed betweenthe second end of the first arc and the first end of the second arc, andthe second half of the transition group is placed between the second endof the second arc and the first end of the first arc, thereby joiningthe first and second arcs to substantially form a circle.
 25. Theunitary inlet structure of claim 23, wherein the stator is comprised of29 stator fins.
 26. The unitary inlet structure of claim 25, wherein theangular spacing of stator fins 1 through 14 is based on substantiallyequivalent spacing for about 30 stator fins, the angular spacing of fin15 is based on spacing for about 29 fins, the angular spacing of statorfins 16 through 28 is based on substantially equivalent spacing forabout 28 stator fins, and the angular spacing of fin 29 is based onspacing for about 29 fins.
 27. The unitary inlet structure of claim 25,wherein the angular spacing of stator fins 1 through 14 is about 12.0000degrees, the angular spacing of stator fin 15 is about 12.4286 degrees,the angular spacing of stator fins 16 through 28 is about 12.8571degrees, and the angular spacing of stator fin 29 is about 12.4286degrees.
 28. A method of manufacturing a Titanium air turbine starterunitary inlet structure comprising: casting a unitary inlet structurefrom an alloy, the unitary inlet structure including: an oversizedannular housing having a longitudinal centerline, at least an air inletand a mounting surface, and an oversized stator integrally formed aspart of the oversized annular housing, the oversized stator disposed atleast partially within the housing and having a plurality of angularlyspaced, circumferentially mounted oversized stator fins connecting thestator to the annular housing; chemically milling the oversized housingand stator to remove alloy from the oversized surfaces thereof;measuring the clearance between the chemically milled stator fins andcomparing the measurements to one or more predetermined values;repeating the chemical milling and measuring steps until at least themeasured clearance between the chemically milled stator fins issubstantially equal to one or more predetermined values.
 29. The methodof claim 28, wherein the stator is transverse to and concentric with thelongitudinal centerline.
 30. The method of claim 28, wherein the alloyis a Ti6Al4V.
 31. The method of claim 28, wherein the angular spacing ofthe stator fins is symmetrical.
 32. The method of claim 28, wherein theangular spacing of the stator fins is asymmetrical.